Many computer workstations used in the office environment today are connected to other workstations, file servers, or other resources over a local area network (LAN). One popular type of workstation is the IBM-compatible Personal Computer (PC) system. One such LAN environment that supports these PCs as "clients" is the Personal Computing Systems Architecture (PCSA) which may be used in conjunction with a DECnet LAN, commercially available from Digital Equipment Corporation, Maynard, Mass., the assignee of the present invention.
Each client PC used in connection with a LAN typically contains one or more internal disk drives and requires its own disk operating system (DOS) to control the internal operation of the PC. For IBM-compatible PCs, the most common operating system is MS-DOS, commercially available from Microsoft Corp., Redmond, Wash.
Each client PC is connected to the LAN via an adapter circuit card which typically supports either a 3COM/Microsoft LAN Manager Network Driver Interface Specification (NDIS) type interface protocol or a Digital Equipment Corporation DEPCA type interface protocol.
A remote boot operation provides support for client PC systems in a LAN environment without requiring each client PC to have a local boot disk properly configured for the network. Remote boot operation allows centralized management of boot disks so that each client PC may be properly configured for operation on the network, i.e., each client PC is booted from a remote boot disk located elsewhere on the network. Additionally, the remote boot process provides support for completely diskless client PC operation. Furthermore, the remote boot process enhances software and network security since the remote boot files may be kept in a secure location and copies need not be distributed among the client PCs.
An approach to the PC Remote Boot process in the PCSA environment is described by Flaherty in U.S. patent application Ser. No. 07/240,955, now U.S. Pat. No. 5,146,568, assigned to the assignee of the present invention. The PCSA remote boot procedure uses virtual Local Area Disk (LAD) technology where the client PC is remote booted off a dedicated virtual disk which resides in a remote networked VAX/VMS server. This approach uses a specially designed remote boot "TASK IMAGE" which is first downloaded to the client PC from the remote VAX/VMS server and is activated by the client PC to establish its network environment, including logical connection to the remote LAD disk. Once the network environment is established, the client PC is booted from the LAD disk as though it were a local device. The network environment established by the TASK IMAGE remains in effect for the remainder of the network session.
This TASK IMAGE is a single segment binary file implementing a network derived from PCSA network components. Since the MS-DOS (or other disk operating system) is not yet in place when the TASK IMAGE is downloaded to the client PC, TASK IMAGE is built as a self-executing binary image, i.e., it does not contain standard MS-DOS executable components. The TASK IMAGE is loaded into the top portion of conventional memory, tightly packed against the uppermost available conventional memory address. Furthermore, the client PC system memory parameters are modified to reflect a smaller available conventional memory space which is adjusted by the size of the now resident TASK IMAGE which must remain active and protected in memory once MS-DOS is loaded and activated.
Once downloaded to the client PC, this TASK IMAGE is activated to establish the network environment under which the PC client will operate, i.e., the PC network environment depends on the networking components included in the TASK IMAGE. As such, this TASK IMAGE is specifically tailored for the type of network adapter used by the client PC. Once established, the network environment running under the TASK IMAGE code remains in effect for as long as the PC client is connected to the network.